Public Safety & Law Enforcement
How to Become a Detective
Most police detectives start as patrol officers: you meet police hiring requirements, graduate from the academy, work patrol for several years (often 3–5), then pass a promotional exam or selection process for an investigative unit. Plan on about 4–7 years in total. Up-front costs are low if a department sponsors your academy, though a criminal justice degree, which many agencies prefer, can cost several thousand dollars or more.
- Time to start
- 4–7 years (police officer first, then promotion)
- Typical cost
- $0–$20,000 (mostly optional college)
- Median pay
- $93,790 per year
- Education
- High school diploma minimum; a college degree is often preferred and sometimes required
- License / certification
- State POST certification as a police officer (private detectives need a state license in most states)
- Job outlook
- 0% (2025–35), little or no change
Steps to become a detective
Decide which kind of detective you want to be
Police detectives work for city, county or state agencies and almost always start as sworn officers. Federal criminal investigators (FBI, DEA, HSI and others) usually need a bachelor's degree and have their own hiring process. Private detectives work for clients or firms and need a state license in most states instead of police certification. Pick your path first, because the steps differ.
Get the education your target agency wants
A high school diploma or GED is the minimum for most local police jobs. Many departments prefer or require college credits for promotion, and federal agencies generally require a bachelor's degree. Criminal justice, criminology, accounting and computer science are useful majors for investigative work.
Get hired as a police officer and complete the academy
Apply to departments, pass the written, physical, psychological and background screening, and graduate from a state-certified police academy. Earn your state POST certification and complete field training. This is the same path as becoming a police officer.
Build a strong record on patrol
Most departments require several years of patrol experience before you can apply for detective, commonly 2–5 years. Write thorough, accurate reports, follow cases to court, and volunteer to help detectives on investigations. Supervisors' evaluations and your report quality often weigh heavily in selection.
Take investigative training
Ask for in-service courses in interviewing and interrogation, evidence collection, search warrants and crime scene work. Many state POST agencies and regional academies offer these. Training in digital evidence, financial crime or crimes against children can open specialized units.
Pass the detective promotional exam or selection process
Depending on the agency, detective is a civil service promotion with a written exam and oral board, or an assignment based on interviews and performance. Study the department's policies, criminal law and investigative procedures listed in the exam announcement. Larger departments may assign investigators first and promote them to detective rank after a set period.
Learn the job in your first investigative assignment
New detectives usually start in property crimes or general investigations before moving to units like homicide or special victims. Work closely with senior detectives, keep organized case files and build relationships with prosecutors. Strong court testimony and case clearance help you advance.
Find a criminal justice program or police academy
A degree is not required for every police detective job, but it helps with promotion and is usually required for federal investigator roles, and many departments reimburse tuition once you are hired.
- Associate degree in criminal justice
- Bachelor's degree in criminal justice, criminology or forensic science
- Police academy (agency-sponsored or self-sponsored)
- Online criminal justice degree for working officers
- Private investigator pre-licensing course (for the PI path)
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How much it costs and how long it takes
| Expense | Low | High | Note |
|---|---|---|---|
| Police academy (agency-sponsored) | $0 | $0 | Most departments pay for the academy after hiring you. |
| Self-sponsored police academy (optional) | $2,000 | $8,000 | Only in states and agencies where self-sponsoring is common. |
| Associate degree in criminal justice (optional) | $3,000 | $15,000 | |
| Bachelor's degree (optional; needed for federal agencies) | $20,000 | $100,000 | Many departments offer tuition reimbursement once you are hired. |
| Promotional exam study materials | $0 | $300 | Agencies list the books and policies the exam is based on. |
| Private detective license, exam and training (PI path only) | $100 | $2,000 | Fees, required training and experience vary widely by state. |
| Total | $25,100 | $125,300 | Timeline: 4–7 years (police officer first, then promotion) |
Exams and how to prepare
Police entrance exams
The written test, physical ability test, psychological evaluation and oral board you pass to be hired as an officer.
How to prepare: Use prep material for the exact written test named in the posting and train to the published fitness standard.
State POST certification exam
End-of-academy exam required to work as a sworn peace officer in most states.
How to prepare: Keep up with academy coursework and review state learning objectives.
Detective / investigator promotional exam
Agency written exam on criminal law, procedure, department policy and investigative techniques, often followed by an oral board or assessment center.
How to prepare: Get the reading list from the exam announcement, study it for 2–3 months, and practice oral scenarios with a current detective.
Private investigator licensing exam (PI path)
Many states require a written exam on state law, ethics and investigative practices before issuing a PI license.
How to prepare: Check your state licensing board for the exam outline and required experience hours.
Prepare for police and detective exams
Promotional exams are agency-specific; the best prep is the reading list in your department's exam announcement.
- Police written entrance exam
- State POST certification exam
- Detective / investigator promotional exam
- Private investigator licensing exam
Detective salary and job outlook
BLS projects little or no change (0%) in employment of detectives and criminal investigators from 2025 to 2035. Openings come mainly from detectives who retire or move up, so competition for detective spots inside departments can be strong. Private detectives earn less on average: BLS reports a median of $51,220 in May 2025.
Source: BLS Occupational Outlook Handbook and Occupational Employment and Wage Statistics, May 2025 data
Printable PDF
Detective Career Kit: 90-Day Action Plan
- 90-day action plan with checkboxes
- Documents checklist
- 12 interview questions with tips
- Resume lines, common mistakes, 13-week tracker
Frequently asked questions
How long does it take to become a detective?
Usually about 4–7 years. You spend 6–12 months getting hired and through the academy, then typically 2–5 years on patrol before you qualify for a detective exam or assignment. Large departments with competitive selection can take longer.
Can you become a detective without being a police officer?
For police detective jobs, almost never; agencies promote from within their sworn ranks. Some agencies hire civilian investigators, and federal agencies hire criminal investigators directly, usually with a bachelor's degree. Private detectives do not need police experience but need a state license in most states.
Do you need a degree to be a detective?
Not always. Many local departments promote officers with a high school diploma, though more agencies prefer or require college credits for promotion. Federal criminal investigator jobs generally require a bachelor's degree.
How much do detectives make?
BLS reports a median of $93,790 a year for detectives and criminal investigators as of May 2025. The lowest 10% earned under $55,390 and the top 10% over $160,540. Federal agents and detectives in large cities tend to earn more.
How do you become a homicide detective?
You first become a police detective, usually starting in property or general crimes, then apply for the homicide unit when an opening comes up. Units look for strong case work, interviewing skills and court testimony. Expect several years beyond your first detective assignment.
How do you become a private detective?
Most states require a private investigator license. Typical requirements include a minimum age (often 18 or 21), a background check, a state exam, and in many states documented investigative experience or approved training. A few states have no statewide license, so check your state's licensing board.
What is the hardest part of becoming a detective?
The long wait and the competition. You need years of solid patrol work, and detective openings are limited, so your reports, evaluations and promotional exam score must stand out. The work itself involves long hours, heavy paperwork and difficult cases.
Is there an age limit to become a detective?
For local police you must usually be 21 to be hired, and some agencies set a maximum entry age. Federal criminal investigator jobs generally require you to be hired before age 37, with exceptions for veterans. There is usually no age limit on promotion to detective once you are a sworn officer.
Sources
- BLS Occupational Outlook Handbook: Police and Detectives
- BLS Occupational Employment and Wage Statistics: Detectives and Criminal Investigators
- BLS Occupational Outlook Handbook: Private Detectives and Investigators
- IADLEST: state POST agencies
- FBI Jobs: Special Agent eligibility
Requirements vary by state and employer and can change. Confirm details with the official sources above before you spend money on training.